The control mechanism disclosed in U. S. Pat. No. 4,541,497 issued to C. W. Riediger, et al. on Sept. 17, 1985, and that was constructed and arranged for steering and operating the transmission of a track-type vehicle, has been well received by the industry. In such mechanism, a tiller arm extends outwardly from a steering assembly which is swingable about an upstanding axis, and the vehicle is steered as the tiller arm is swung in either direction away from a generally centered neutral position.
As is further disclosed in U. S. Pat. No. 4,798,099 issued to G. F. Alexander, et al. on Jan. 17, 1989, the aforementioned tiller arm is preferably arranged so that an operator's left hand can twist either a directional actuating member or a juxtaposed speed actuating member about an outstanding axis of that tiller arm. In this way the vehicle operator can limitedly rotate the directional actuating member to change the direction of the vehicle or to effect neutral, and/or can rotate the speed actuating member to a selected gear ratio while simultaneously steering the vehicle by pushing or pulling the tiller arm. For example, the tiller arm can be conveniently grasped by an operator's downwardly facing left-hand palm as the vehicle is traveling forwardly and swung forwardly to steer the vehicle to the left. At the same time the vehicle can be shifted from forward to reverse by merely twisting the directional actuating member about its own axis through a relatively limited range.
U. S. Pat. No. 4,796,736 issued to D. M. Fee, et al. on Jan. 10, 1989 teaches a further advancement of the control mechanism mentioned above. Specifically, a parking brake actuating member is pivotally mounted on the steering assembly and is manually movable between BRAKE-OFF and BRAKE-0N positions. When the brake actuating member is moved to the BRAKE-ON position, a coupling apparatus associated therewith is effective to urge the directional actuating member to the neutral position. This prevents inadvertent movement of the vehicle by the transmission when the brake actuating member is subsequently placed in the BRAKE-OFF position.
As is disclosed in the aforementioned U.S. Pat. No. 4,541,497, swinging movement of the tiller arm and associated steering assembly away from neutral is mechanically translated to corresponding movement of a steering selector spool of a steering control valve. The axial displacement of that steering spool subsequently controls the flow of hydraulic fluid between an engine driven steering pump and a reversible steering motor. Even if the directional actuating member is placed in the neutral position such that the transmission is not powering the cross drive mechanism or transaxle, the steering system is still active. Particularly, the positioning of the tiller arm forwardly by the operator with the transmission neutralized could cause the vehicle to turn to the left by counterrotating the left and right tracks, and to thus make a spot turn in a counterclockwise direction about its own central vertical axis.
In order to prevent inadvertent movement of the vehicle upon restarting the engine after a shut-down, in the event that the tiller arm and steering assembly is displaced from the neutral position, it is desirable to provide a reliable indexing device for assuring the steering assembly is positively in neutral at restart. Such an indexing device should preferably be integrated with the parking brake actuating member, and should provide a feedback to the operator that the steering assembly is truly positioned in neutral. Moreover, the indexing device should preferably assure that the elements between the steering assembly and the steering selector spool are properly adjusted. And, still further, the indexing device should preferably prevent restarting of the engine if the indexing device is not engaged in the neutral mode, and be of simple and reliable construction.
The present invention is directed to one or more of the problems as set forth above.